Material reducing machines are used to reduce waste materials such as trees, brush, stumps, pallets, root balls, railroad ties, peat moss, paper, wet organic materials and the like. Two common types of material reducing machines include grinders and chippers. Grinders are typically configured to reduce material through blunt force impactions. Thus, the reduced material product generated by grinders generally has a ground, flattened texture with relatively high fines content. This type of reduced material is typically used as mulch. In contrast to the blunt force action used by grinders, chippers reduce material through a chipping action. The reduced product generated by chippers preferably has a relatively small percentage of fines. This type of chipped reduced product can readily be used as fuel for a burner since the material is more flowable than ground reduced material and can easily be handled by the material processing equipment used to feed fuel to a burner.
Two common types of grinders include tub grinders and horizontal grinders. Example horizontal grinders are disclosed in U.S. Pat. Nos. 7,461,832; 7,441,719; 5,975,443; 5,947,395; 6,299,082; and 7,077,345. Example tub grinders are disclosed in U.S. Pat. Nos. 5,803,380; 6,422,495; and 6,840,471. Example wood chippers are disclosed in U.S. Pat. Nos. 5,692,548; 5,692,549; 6,290,115; 7,011,258; 5,005,620; 3,542,302; and 3,861,602.
Grinders typically include reducing hammers on which replaceable grinding cutters (i.e., grinding tips or grinding elements) are mounted. Grinding cutters generally have relatively blunt ends suitable for reducing material through blunt force impactions. In contrast to the grinding cutters used on grinders, chippers typically include relatively sharp chipping knives configured to reduce material through a cutting/slicing action as opposed to a grinding action. An advantage of grinders is that grinders are generally suited to better tolerate wear than chippers without unduly negatively affecting the performance of the grinders and quality of the product output by the grinders. An advantage of chippers is that the sharpness of the chipping knives allows certain materials (e.g., trees) to be processed more rapidly with less power than would typically be required by a grinder.
The reduced products generated by chippers and grinders can be used for a variety of applications. For example, the reduced product is often used as mulch and is also used as fuel for a burner. For at least some of these applications, it is desirable for the reduced material to have pieces of generally uniform size.